Electromagnetic switching system



May 10, 1949. w. A. RAY 2,469,609

ELECTROMAGNETIC SWITCHING SYSTEM Filed Jan. 1, 1944 RECTIFIER 13 I2 cgfiiil -32- 1 I4 DEVlCE' 6 21 '7 DEVIFE Snnentor;

WILLIAM A. RAY,

(Ittorneg.

Patented May 10, 1949 ELECTROMAGNETIC SWITCHING SYSTEM William A. Ray, Los'Angelcs, Califi, assignor to General Controls 00., a'corporation Application January 1, 1944, Serial No. 516,733

5 Claims. 1

My present invention relates to electrical control systems, and more particularly to such systems which include electromagnetic conditioncontrolli'ng devices.

An object of this invention is to provide, in a direct-current-energized electromagnetic device comprising a core and armature attractable thereby, means for overcoming the effect of remanence of the core tending to retain the arme ture in attractedrelation thereto upon cessation of the current- Another object lstoprovide', in asystem wherein an alternating current circuit is controlled by an electromagnetic switching device energized by rectified alternating current, means for sub-- jecting the electromagnetic device to an alternating flux to ensure proper demagnetization thereof when the rectified alternating. current is interrupted.

There are well-known control systems, energized by alternating current from the service lines, which include electromagnetic devices, of the manual reset safety type energized by a rectified component of the alternating current such as that produced, for example, by a vacuum tube amplifier, a photoelectric cell, or a conventional rectifier. The manual-reset device acts, upon the establishment of an abnormal or unsafe condition in the system, to interrupt the electrical energy and, as the name implies, must be manually reset in order to reinitiate operation of the system. In the event of temporary interruption of the electric service, or line failure, the manual reset device responds in the samemanner as it would had an unsafe condition been established; hence the unwarranted attention of an operator is required after each occurrence of a line-failure. It is therefore another object of this invention to so improve a system of the character described that the man ual-reset device is unaii'ected by ordinary line'- failure and responds only to the establishment of the unsafe condition.

Other objects and advantages" of the invention will be found in the description, the drawing, and the claims; and, for full understanding of the invention, reference may be had to the fol lowing detailed description and accompanying,

drawing, wherein: a

Figure 1 is a diagrammatic'view of a control system embodying the invention; and

Figures 2 and 3 are views of the electromagnetic switching device of Figure 1, showing the parts in different positions assumed in operation.

To facilitate understanding of thesystem of Figure 1, the electromagnetic switching device shown in Figu-res l,- 2 and 3 will first be described per se. The numeral H indicates a U-shaped electromagnet'core, around one side arm of which is an energizing coil I2; Around the other side arm of the core is another coil l3 for a purpose hereinafter to be described and which for the present can be disregarded; Cooperable with the pole" faces at the ends-of core II is an armature l4 having-a dependent stem. I5 towhich is secured an. insulating collar l6 which carries a flexible contact blade ll. Aligned with stem: I5 is another stem H? having, secured thereto, an insulating collar lewhi'ch carries a bent contact member 20; The stems i5 and it are reciprocable in openingsthrough fixed plates 2| and 22, respectively, and are limited in the direction of downward movement by engagement of their collars i6 and i9 with these plates. Encircling the stern I8, and compressed between the underside of plate 22' and a button 23 at the bottom end of the stem, is a spring 24.

As shown in Figure 2, core H is deenergized and the armature M is therefore in released position, to which position, it is to be assumed, it was moved by gravity; It will be noted that in thisfigure the hooked portion 25 of the contact member 20 is out of engagement with contact blade H;

In Figure 3, the armature I4 is shown as being manually held in engagement with core H (as indicated by the finger 26) after having been moved to that position through the medium of stem l8. It will be noted that in this figure the contact hook 25 is spaced slightly farther from blade I? than it was in Figure 2. If, while core H is unenergized, the reset button 23 is released, the part's'return to the positions shown in Figure? without engagement of the contacts.

In'Figure 1, the parts are shown in the position'which they-reach in the event that core H was energized before and after the reset button was released-the stem l5 being retained in elevated position due to the magnetic attraction of armature M by the core, so that the contact hook-- is in firm engagement with contact blade 11, which is flexed under the force of spring 24.

If core i l is now so deenergized that the armature is released, the parts return to the positions shown in Figure 2; manual-resetting of the armature (and reenergization of the core) being necessary before the switching mechanism can be reclosed.

A manual-reset electromagnetic switching de-- vice, of. the same general character as that described above, is disclosed in Patent No. 2,237,577, granted to me April 8, 1941. The device of that patent includes valve means, operated by the movement of the armature, for controlling, by way of example, supply of gas to a pilot burner for a main burner; the switching means serving to effect energization of an electrically operated valve for the main burner only in the event that the armature is held in attracted position, as when the core is energized by the passage through its coil of current generated by a thermoelectric device heated by the pilot-burner flame.

Referring now to the control system shown in Figure l, the nurneral 30 indicates a step-down transformer, the primary of which is connected to wires 3| which represent ordinary alternatingcurrent service lines. The secondary of the transformer is connected to wires 32 which lead to a load, here illustrated as an electric fluidcontrol valve 33, in series with a switching device 34 (designated by the legend as an Automatic control device) and the contact members 35-35 of an electromagnetic relay 37. The control device 34 may be such as a thermostat, pressurestat, or the like, responsive to a condition normally resulting from the operation of the valve 33.

One lead of the energizing coil l2 of the manual-reset device is connected directly to one of the power wires 32; the other lead of coil l2 being connected, in series with a Safety control device 38 and an alternating-current Rectifier 3%. to the other of the wires 32. The device 38, as the legend suggests, is responsive to an abnormal or unsafe condition of the systemsuch as excessive temperature or pressure, low level of water in a boiler, or extinguishment of the flame of a pilot burner for a main burnerand acts, upon establishment of the abnormal condition, to interrupt the circuit of coil [2 in which it is connected. The rectifier 39 may be of any known type, such as one which includes a vacuum tube or dry disk elements; and, while for the sake of simplicity it is shown as being connected directly in series with the device 38 and coil l2, it is to be understood that if it is of the full-wave or bridge type, it will be connected in a well-known manner across the alternating current lines. It is further to be understood that the rectifier may include smoothing means (such as a capacitor) so that substantially uninterrupted direct current is produced. The safety control device 38 may be self-rectifying (as, for instance, when it comprises a photoelectric cell) and no additional rectifier is then required.

The additional coil I3 is connected by one of its leads directly to one of the power wires '32; its other lead being connected to the contact blade H which, as shown in Figure l, is in engagement with the hook 25 of contact member 2!]; this member being connected, in series with the coil 48 of relay 37, to the other of the power wires 32. In short, coil i3 is normally connected across the power wires in series with the relay coil and the switching mechanism of the manualreset device.

The electromagnet of the manual-reset device in the system illustrated diilers from those of similar devices commonly in use in that core H is of such character that its remanence (or residual magnetism) is sufficient, when the flow of direct or rectified alternating current through coil I2 is interrupted, to maintain the armature M in elevated (or attracted) position against the '4 force of gravity acting upon it. Hence, in the absence of coil [3, the switching mechanism would at all times remain in the closed condition of Figure 1. However, due to the flux produced in core II by flow of alternating current through the coil l3, the core is substantially demagnetized when current flow through coil 12 is interrupted, so that the armature is then released; the parts assuming the positions shown in Figure 2 wherein the switching mechanism is open. The coil [3 is so designed that the alternating flux produced thereby is relatively weak and insufficient to affect normal operation of the electromagnet. While it is usually preferable to so arrange the armature and the polefaces of the core that their surfaces come into direct contact, if the remanence of the material of which these parts are constructed is relatively great, a thin non-magnetic separator (as of copper) may be provided between the surfaces to aid release of the armature by the demagnetizing force.

As shown in Figure 1, the parts are in the positions in which they remain during normal operation of the system; load 33 then being operated in accordance with the demand of the automatic control device 34.

If, during continuance of normal electric service, the safety control device 38 acts, in response to the establishment of an abnormal condition, to interrupt flow of current through coil l2, the armature is released as described above; the resultant opening of contacts I1 and 25 effecting deenergization of relay 3! so that its contact element 36 is released, thereby opening the main circuit constituted by load 33, automatic control device 34, and the secondary of transformer 30. To reinitiate operation of the system after the cause of the abnormal condition has been remedied, the manual-reset device is operated as described hereinbefore. It will be observed that since, by the particular switching mechanism shown, the circuit of the demagnetizing coil I3 is completed only upon retraction of the reset button, the setting of the armature in magnetic engagement with the core is facilitated; this feature having particular value when the current available for supplying coil 12 is relatively weak, such as that produced by a photoelectric cell.

In the event of interruption of the electric service, or line-failure, coil I2 is deenergized, but since coil [3 is also deenergized, the armature is retained in attracted relation to the core. However, the main circuit is then in the same deenergized condition as it would be in response to the release of the armature, and the system is hence safe. Upon resumption of electric service, both of the coils I2 and I3 are energized simultaneously and the armature therefore remains in engagement with the core, so that resetting is not required and the system functions automatically as before the line-failure. If during the absence of electric service an abnormal condition had been established, the armature would be released immediately upon resumption of service and resultant energization of the demagnetizing coil.

The relay 31 is not an essential element of the system since the main circuit (of load 33) could be connected directly in series with the switching mechanism contacts H and 25, and the demagnetizing coil 13. However, provision of the relay is desirable since the amount of current then flowing through the demagnetizing coil is substantially constant regardless of the resistance of the particular load 33 employed.

The demagnetizing coil I3 could be connected directly across the power wires 32 instead of in series with the switching mechanism and relay or load (contact blade l1 then being connected to the right-hand one of wires 32); however, by connecting the demagnetizing coil as shown, the safety of the system is assured in the event of possible break-down of this coil or opening of its connections (which would render release of the armature impossible) since the circuit of the relay or load would also then be open.

The provision of means for demagnetizing the core also has utility in connection with a manualreset electromagnetic device of conventional type wherein the armature is released upon cessation of the energizing current, particularly if the flux produced in the electromagnet is relatively weak (as when a thermoelectric generating device heated by a small pilot-burner flame is employed) and the ratio of holding-flux to residual-flux is therefore low.

The embodiment of my invention herein shown and described is obviously susceptible of modification without departure from the spirit of the invention, and I intend therefore to be limited only by the scope of the appended claims.

I claim as my invention:

1. In a system for controlling the energization of a load by A, C. from a source thereof: an electromagnetic device comprising a core member and a cooperating armature member; a source of D, C. for energizing said electromagnetic device; a rectifier, energized by A. C. from said source thereof, for providing said source of D. C.; means for controlling the energization of said electromagnetic device; said electromagnetic device being so designed that while energized it is capable of retainin the armature member in attracted position when the armature member is first brought to that position but is incapable of attracting the armature member from its unattracted or released position, the armature member being biased to said unattracted position; one of said members of the electromagnetic device being of material whose remanence in relation to the armature-member bias is such as to eifect retention of the armature member in attracted position when the electromagnetic device is deenergized; demagnetizing means normally continuously applying a demagnetizing force to said one of the members in an amount only sufiicient to effect release of the armature member when the electromagnetic device is deenergized, said demagnetizing means being energized by A. C. from said source thereof so that in the event of failure of that source the armature member is then retained in attracted position despite the coexisting deenergization of said rectifier; and switching means, actuated by movement of the armature member, for controlling the energization of said load.

2. A control system as defined in claim 1, wherein said means for controlling the energization of said electromagnetic device comprises condition-responsive means acting upon establishment of an abnormal degree of said condition to effect deenergization of the electromagnetic device, and said switching means is so actuated in response to release of said armature member as to efiect deenergization of said load.

3. A control system as defined in claim 1, wherein said switching means is arranged to effect deenergization of said demagnetizing means in response to the release of said armature member.

4. A control system as defined in claim 1, wherein said demagnetizing means is so arranged, for energization by A. C. from said source thereof, in series with said load that the load is unenergizable in the event of open-circuiting of the demagnetizing means.

5. A control system as defined in claim 1, wherein said load is an electrically-operated switching device, and said demagnetizing means is arranged in series with said load for energization by A, C. from said source thereof.

WILLIAM A. RAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,015,968 Lehr Jan. 30, 1912 1,301,412 Elmen Apr. 22, 1919 1,314,332 Jones Aug. 26, 1919 1,424,140 Replogle July 25, 1922 2,164,694 Betz et a1 July 4, 1939 2,260,810 Jones Oct. 28, 1941 2,287,617 Jones June 23, 1942 2,297,339 Wilms Sept. 29, 1942 2,351,277 Mantz June 13, 1944 FOREIGN PATENTS Number Country Date 16,359 Great Britain July 19, 1906 

